Halogen-containing polymers or plastics or molded articles produced therefrom tend to undergo substantial changes during their production process and under environmental influences. For example, they tend to decompose and degrade under the influence of heat and/or light. The degradation of such halogen-containing polymers, in particular PVC, produces halogenic acid (in case of PVC hydrochloric acid), which is eliminated from the polymer strands, resulting in a discolored, unsaturated plastic having chromophoric polyene sequences.
To avoid these undesirable changes, it is common practice in the art to add stabilizers to these polymers that at least partially prevent decomposition and/or discoloration first during the production process and then later on during the lifetime of the product. In the past, toxic heavy metal-containing compounds, such as lead, barium or cadmium containing compounds, have been used as stabilizers. However, due to the toxicity and environmental concerns, in the recent years, attempts have been made to find alternative stabilizers. Today a growing number of heavy metal-free stabilizer compositions is available, including among others, hydrotalcites, perchlorates, alkaline earth metal oxides, hydroxides and carboxylates, etc. Other known stabilizers include nitrogen-containing compounds, such as aminouracils and isocyanurates.
THEIC (Tris-hydroxyethylene-isocyanurate), for example, is well known and well used in stabilization of halogenated thermoplastics, especially PVC. The mode of action is not completely elucidated, but it is hypothesized that THEIC as a polyol complexes Zinc cations and thus delays the formation of the Lewis acid [ZnCl4]2− which catalyzes the degradation of PVC-polymer chains.
Despite numerous stabilizer compositions being known and available, there is still need for alternative stabilizers with improved properties, for example with respect to initial coloring and color stability, while being environmentally safe and non-toxic.